1. Field of the Invention
The present invention relates to a rangefinder device for use in an auto-focus camera or the like, and more particularly to improvements in or to a rangefinder device having a function of detecting that improper distance measurement through glass or the like has been performed, and a camera that incorporates such a rangefinder device.
2. Description of the Related Art
In a conventional active type rangefinder device, a signal beam is projected towards an object whose range is to be determined (the xe2x80x9ctarget objectxe2x80x9d) by a projecting section, the reflected light therefrom is received by a light receiving section which is arranged at a specified distance corresponding to a base length from the projecting section, and the distance to the target object is calculated from the light receiving position (the reflected spot position).
However, if glass is present between the photographic subject and the camera, a reflected signal beam is generated by the surface of the glass, so that it has been difficult to focus upon a photographic subject on the other side of a glass barrier.
Moreover, as a countermeasure when performing photography through glass with a conventional active type rangefinder device, there have been proposed a method of determing that photography is being performed through glass if a light reception output is obtained when distance measurement is carried out with a combination of of light projection/reception elements different from a regular combination of light projection/reception elements by using an active multi-point type rangefinder device, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 6-51191, and a method in which the presence of glass is detected from the value of the amount of received light and depending upon whether a ranging output falls within a ranging interlock range, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 8-219772, for example.
However, with the active type range finders described in the above-mentioned Japanese Laid-Open Patent Publications (Kokai) Nos. 6-51191 and 8-219772, it is only possible to determine upon the presence of glass only in such a case where the glass is at a very close distance. In other words, there has been the problem that it has not been possible to make a correct determination if the glass is positioned at a certain or considerable distance from the camera, and regular reflected light of an IRED reflected from the glass is incident upon the light receiving element.
It is an object of the present invention to provide a rangefinder device which is capable of detecting that improper distance measurement through glass or the like has been performed, even when the glass is positioned at a certain or considerable distance from the camera, and a camera incorporating the rangefinder device.
To attain the above object, a first aspect of the present invention provides a rangefinder device, comprising a projecting section that projects a signal beam towards a photographic subject, a light receiving section that receives light from the photographic subject due to the projection via two different light paths, a distance information calculating circuit that calculates distance information related to a distance to the photographic subject from a positional relationship between images received by the light receiving section, a position calculating circuit that calculates first position information related to positions of the images received by the light receiving section based upon the calculated distance information, and a determination circuit that determines whether the calculated distance information is proper or improper, from a relationship between the first position information calculated by the position calculating circuit and second position information related to light receiving positions of the images that is obtained based upon an output from the light receiving section.
Preferably, the light receiving section has a first light reception range and a second light reception range that is separated by a predetermined base length from the first light reception range, and the light receiving section receives light from the photographic subject at the two light reception ranges at angles corresponding to the distance to the photographic subject.
Preferably, the rangefinder device according to the present invention comprises a position detecting circuit that detects the second position information related to the light receiving positions of the images that is obtained based upon the output from the light receiving section.
In a preferred form of the present invention, the determination circuit determines that the calculated distance information is proper when a degree of agreement between the first position information and the second position is higher than a predetermined value, and that the calculated distance information is improper when the degree of agreement is lower than the predetermined value.
Preferably, the rangefinder device according to the present invention comprises a distance determining circuit operable when the calculated distance information is determined to be improper, for setting the distance to the photographic object calculated by the distance information calculating circuit based upon light from the photographic subject received by the light receiving section in a state with projection operation not being performed by the projecting section, as an effective result of distance measurement. Alternatively, the distance determining circuit may designate a predetermined distance value for the distance to the photographic subject when the calculated distance information is determined to be improper.
To attain the above objective, a second aspect of the present invention further provides a camera having a rangefinder device comprising a projecting section that projects a signal beam towards a photographic subject, a light receiving section that receives light from the photographic subject due to the projection via two different light paths, a distance information calculating circuit that calculates distance information related to a distance to the photographic subject from a positional relationship between images received by the light receiving section, a position calculating circuit that calculates first position information related to positions of the images received by the light receiving section based upon the calculated distance information, and a determination circuit that determines whether the calculated distance information is proper or improper, from a relationship between the first position information calculated by the position calculating circuit and second position information related to light receiving positions of the images that is obtained based upon an output from the light receiving section.
To attain the above object, a third aspect of the present invention also provides a rangefinder device for use in a camera, comprising a projecting section that projects a signal beam towards a photographic subject, first and second light receiving sections that each receive light from the photographic subject, a distance information calculating circuit that calculates distance information related to a distance to the photographic subject from a phase difference between light receiving positions of images obtained by the first and second light receiving sections, a light receiving position detecting circuit that detects light receiving positions of the images obtained by the first and second light receiving sections, and a determination circuit that calculates light receiving positions from the distance information calculated by the distance information calculating circuit, and compares the calculated light receiving positions with the light receiving positions detected by the light receiving position detecting circuit, to thereby determine whether reflected light from a substance that is transparent to light has been received by the first and second light receiving sections.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.